Cupolas what is the truth?

[Cindi]

I am finally going to Oregon and will be building my geodesic dome as soon as I can find some property to purchase.  I found this FB group of dome home owners and they seem to think Cupolas are mandatory for air circulation.  Here is what one of them said:

"If you don’t have a cupola on top of your dome house there is no proper circulation of air and heat and moisture will accumulate. Depending on the outside and inside condition there is a good chance that the dew point will be in the material you covered your dome with. That will be the perfect condition for rot in your wood to the point of a dangerous situation. It can develop unnoticed over a longer period until it is to late." 

and another one said: 

"It prevents the condensation of moisture in the air thru "overpressure" or "hot roof". Put a glass bowl open end down in the sun and watch the water droplets form. Drill some holes, Now you have a colander but the droplets don't form. All the small cracks between the panels allows the heated air to move up. Keep it in the envelope and what happens?"

I swear I read somewhere that domes can breath naturally and provide their own constant airflow, in through the bottom, up to the top, down the middle and out the bottom.  Now I realize this would require some type of venting like an air intake vent. 

What do you all think?

Thanks! 

Cindi

[Cindi]

Thank you so much I will check into that.  

On Sunday, August 15, 2021 at 12:59:28 PM UTC-4 clark.rob...@gmail.com wrote:

Instead of a cupola, consider a heat recovery system such as the Lunos through the wall unit.  It will provide fresh air and control the humidity inside your home without venting heat to the outside.  I have the Lunos in my air-tight SIP house and it took care of the humidity problem I had the first winter.  A pair of units acts as lungs alternately breathing in and then out in one minute intervals.  Heat is stored and then recovered in a ceramic core.  Very quiet.  Supposedly 85 to 90 percent efficient.

-Robert

[Blair Wolfram]

Hello Cindi;

Following is information about dome cupolas. 

Basic condensation science is warm moist air condenses on cool surfaces. This is science and happens 100% of the time every time. The best way to prevent excess moisture from condensing on any surface including windows is to identify where the moisture originates and remove the moisture at its source. If you take long hot showers and don't have or don't use a bathroom exhaust fan the steam moisture as water vapor will be trapped inside and rise into the house, and eventually condense. If you run an exhaust fan during and for maybe 20 minutes after you shower you will drastically reduce condensation problems in your home whether the home is round or square. The same is true from cooking and boiling water; if you run a hood vent or kitchen exhaust fan you will eliminate air-borne moisture and condensation will be minimal. 

Warm air can carry more moisture than cooler air. When warm air meets cool air a dew point is established as the warm air cools and loses its ability to hold as much moisture and releases moisture onto any cooler surface. If you have an insulation barrier between heated indoors and cold outdoors, (or where cooler indoor air meets hot outside air) the dew point is somewhere inside the insulation wall. This becomes a problem with open-cell insulation such as fiberglass and cellulose. Moisture can be removed by circulating air across the surface of the open cell insulation. Closed cell insulation such as spray-on extruded polyurethane or rigid styrofoam boards doesn't allow moisture to penetrate into the insulation, so where the warm air meets cooler air a dew point is still established but there is no water vapor or moisture that reaches to this point and condensation does not occur.

A "hot roof" is a design with closed cell insulation installed tight to the inside surface of the exterior plywood roof deck, and for the reason described above doesn't have a ventilation need for the insulation.

Three types of cupolas may be used in dome construction. A vent cupola (see 4th pic attached) is used in a system which allows air in the dome insulation cavity inside the dome walls to escape and exhaust out into the atmosphere, exactly as attic ventilation in conventional homes is designed. Air enters a conventional home attic through soffit vents around the lower edges of the roof, circulates across the insulation surface on the floor of the attic, and leaves through a ridge vent along the peak of the roof. This system will remove moisture from open cell insulation such as fiberglass and cellulose and will help maintain its insulation quality. In a ventilated dome built with fiberglass insulation, ventilation air enters the dome shell insulation space along the lowest dome edge where the dome sits on the riser wall or base foundation similar to a soffit vent. The insulation cavity must allow air to circulate horizontally and vertically through and past all the struts with vent holes or vent notches, and exits at the top of the shell through the vent cupola acting as the ridge vent. The performance of fiberglass insulation is outperformed by urethane insulation, but if you prefer fiberglass both Dome Incorporated and Natural Spaces offer a ventilated dome shell as an option. A ventilated shell also helps cool a dome's heat gain in hot climates by drawing air across the inside surface of the exterior plywood roof surface and exhausts heat generated by the shingles, reducing the air conditioning load.

If the dome uses closed cell polyurethane insulation, shell ventilation isn't required. Building codes in most of the U.S. require ventilation when fiberglass insulation is used as roof insulation, and in a dome there is no change in the science.

A view cupola (see 1st and 2nd pic attached) is part of a vent system, and is located at the top of the dome where operable windows open and allow air to naturally rise up and out of the interior living area in a dome. This design also cools a dome in the summer allowing warm air that has collected at the top of the dome ceiling to escape up and out. For adequate cooling a power vent may be installed at the top of the dome. Air enters the living space through awning windows in the riser wall.

In colder climates the view cupola sometimes acts like a thermos bottle with the top left off. The warmest air in the home rises up to the cupola and meets the low r-value windows instead of high r-value insulation, allowing heat to escape.

A vent cupola may be designed to exhaust interior air also, as shown in the 3rd pic attached as ventilation in a large horse barn. 

The best solution to prevent moisture in domes is to eliminate the water vapor at its source through dedicated use of bathroom and kitchen exhaust fans.

Blair

Founder, www.domeincorporated.com

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[Levente Likhanecz]

hi Cindi,
okay, it is not the "green way" because consuming electricity.

https://www.amazon.co.uk/20L-Dehumidifier/s?k=20L+Dehumidifier

but a 300-400W dehumidifer can dry up your living area like desert.
and it is able to pull out all moisture from carpets, textiles,
cardboard decors, plaster.
i have a very unventable house, and i have to use 1 of these all
winter, but very effective.

them have usually a smaller capacity heatpump (airco or fridge style).
the cold end condenzating rapidly the air, while the hot end just
heating the room. so the heayed back air can absorb more humidity from
the room.
cheers, lev

[Cindi]

Hey Lev!

I like Robert's suggestion, I will add these to the dome and the rooms.

[Levente Likhanecz]

okay,
if no excessive dusting problem around your area, then the heat
retaining air exchanger an excellent solution.

cheers, lev